1. Field of the Invention
This invention relates to signal isolators and more particularly to an analog signal isolator utilizing optical couplers in a switching mode to provide electrical isolation between its analog input and output.
2. Description of the Prior Art
The prior art analog isolators or couplers using optical coupling normally operate the optical couplers in a linear region. This may require use of a feedback circuit around the coupling devices and normally an additional pair of optical couplers to provide stable signal reproduction. When the optical couplers are used in a linear mode, matching operating characteristics of these devices is critical.
U.S. Pat. Nos. 3,315,176; 3,590,251; 3,327,239 and 3,893,037 are exemplary of devices which utilize various types of optical couplers in their linear range. In addition U.S. Pat. No. 3,893,037 illustrates the use of optical couplers for feedback signal coupling. U.S. Pat. No. 3,810,034 discloses an apparatus for transmitting DC signals from an input circuit to an electrically isolated output circuit. For transmission of an analog signal the photo coupling devices in U.S. Pat. No. 3,810,034 would have to operate in a linear range.
Prior art devices which use optical coupling for providing electrical isolation usually operate the optical coupling devices in their linear range. The photo coupling devices when operated in their linear range cause the circuit to be sensitive to various operating characteristics such as linearity, gain, temperature sensitivity and other device parameters. Thus, matching and selecting characteristics of necessary photo coupling devices becomes a major problem.